The present invention relates to an automatic sampling device and, in particular, to a device that automatically transfers a sample container from a sample tray to known laboratory analyzing equipment, for the examination of, for example, the heats of transformation of a sample, and which transfers the sample container from the analyzing equipment to the sample tray.
It is known to use thermal gravimetric analysis (TGA) systems to conduct thermal analyses of selected samples, also referred to herein as specimens, in order to examine certain characteristics of the samples as a function of temperature. As it is sometimes necessary to carry out measurements on a large number of samples, it is desirable and known in the art to mechanize the manipulation of the specimens. Such mechanization is commonly referred to as autosampling.
One autosampler is shown in U.S. Pat. No. 5,398,556 to Lang. Lang discloses a device having a vertical gripper member and a rotatable specimen plate for holding a plurality of specimen containers. A specimen container is transferred to the measuring location in the parent machine (e.g., a TGA) by rotating the specimen plate so that the desired specimen container is positioned under the gripper. Then, the gripper, which is driven by a motor, is lowered and gripping fingers attached to a gripping member grip the specimen container. The container is then raised from the specimen plate by raising the gripping member. The specimen plated is then rotated until a recess in the specimen plate is located underneath the gripping member. Next, the gripping member is lowered through the recess in the specimen plate and the specimen container is placed at the measuring location, which is directly underneath the gripper. The specimen container is then deposited on the measuring location by releasing the gripper fingers.
A disadvantage of the gripper taught by the Lang patent is that the device is relatively complicated in that it has many moving parts and that if the motor over- or under-drives the gripper, an error could occur in the placement of the sample.
In conventional thermogravimetric analysis machines, samples are placed in a crucible or sample container that is positioned in a furnace on a platinum ribbon attached to an automatic recording balance. Conventional TGAs are disadvantageous because the platinum wire is easily bent with even a very small force by the gripper when it moves the crucible on and off the balance. After the platinum wire is bent, it is virtually impossible to move back into its original position. If the device is used with a bent wire, it is extremely difficult to accurately position the crucible within the furnace. Further, the act of replacing the platinum wire typically decreases the sensitivity of the machine and detrimentally effects its performance.
Known autosamplers are also disadvantageous because static electricity may accumulate in the furnace area. This is frequently a serious problem which detrimentally effects analytical results. The static buildup generally occurs on the surface of the glassware surrounding the TGA furnace and is aggravated by movement of the glassware over insulating material, such as an O-ring. The resulting electrostatic fields attract the sample container to the surface of the glassware, thus moving the sample container off balance and jeopardizing the advancement of the analysis. Additionally, static electricity may pull some of the sample from the sample pan if the sample pan contains some dust-like particles.
Devices and methods are known to reduce or eliminate static electricity. For example, there are solutions which may be wiped onto glass surface areas. Unfortunately, these known solutions may leave behind a residue which can undesirably build-up on the glass and adversely effect the test results. Alternately, an operator may point a hand-held ion generating device at the area. However, such is undesirable because it requires the operator to stay in the vicinity of the autosampler during the course of the sampling, which can be many hours, and, because the static electricity is not visible, the operator may miss the problem area. Additionally, radioactive emitters are available. However, these are disadvantageous because they have strict disposal requirements.
As is known, conventional autosamplers comprise a sample tray table having a plurality of recesses for holding each of the sample containers in place while the analysis is being conducted. Conventional sample tray tables, however, are disadvantageous because they do not facilitate placement of the sample pan into the recess.
Sometimes it is necessary to work with sealed sample containers, such as when the contents of the sample container are volatile. If a sample container is sealed, it is necessary to puncture the top of the sealed container prior to placing it into the furnace. Conventional puncturing devices are disadvantageous, however, because they have several moving parts and are relatively complicated. Further, disadvantageously, it is sometimes necessary to puncture a sample manually before it is loaded into the tray. When this is done, the sample sometimes loses some of its properties before being loaded into the furnace.
What is desired, therefore, is an autosampler which has a gripper assembly that cooperates with a hanging wire, wherein the hanging wire is not easily bent or damaged and wherein the hanging wire may be easily replaced without reducing the sensitivity of the parent instrument, which is operably connected to an electrostatic discharge device, which has a sample tray table with recesses that facilitate placement of the sample container into the recesses, and which is operatively connected to a safe and reliable puncturing device.
Accordingly, it is an object of the present invention to provide an autosampler which has a gripper assembly that cooperates with a hanging wire which is durable and not easily damaged.
It is another object of the present invention to provide an autosampler which cooperates with a hanging wire assembly that can be easily replaced without reducing the sensitivity of the parent instrument.
It is still another object of the present invention to provide an autosampler which has a sample tray table with beveled edges and rounded recess areas to facilitate placement of the sample pan into the recesses of the sample tray table.
It is yet a further object of the present invention to provide an autosampler which is operatively connected to an electrostatic discharge device that is safe, effective and easy to use.
It is still another object of the present invention to provide an autosampler which is operatively connected to a puncturing device which has no motorized parts and which is relatively inexpensive to manufacture and simple to construct.
It is still a further object of the present invention to provide an autosampler which is reliable, easy to use, and cost-effective to manufacture and maintain.
To overcome the deficiencies of the prior art and to achieve the objects and advantages listed above, an autosampler is disclosed which comprises a novel gripping assembly which is uniquely sized and shaped to stabilize a crimped wire which hangs from an arm of a balance of the parent instrument. After the gripping assembly grips and stabilizes the wire, a tray table which is positioned about the gripping assembly, moves vertically and rotationally to position a specimen container onto a hook at the bottom of the crimped wire and substantially reverses its steps to remove the container from the crimped wire.
The crimped wire is uniquely designed to be received by the gripping apparatus. The crimped wire has two ends defining an axis therebetween and has at least one point which is displaced from the axis, i.e., the hanging wire is substantially bent at at least one location.
More particularly, the gripper assembly comprises upper, middle and lower gripping fingers, which are movable between an open and a closed position. The upper and lower fingers each have a V-shaped portion at one end for receiving the crimped wire therein and aligning the crimped wire above and below its bend. The middle gripping finger has two ends and is positioned between, and opposed to, the upper and lower gripping finger. The middle gripping finger has a portion at one end thereof sized and shaped to receive the crimped wire at the bend. When the gripping fingers are in the closed position, they grip the crimped wire and stabilize it while the specimen tray moves so as to connect the specimen container to the hook of the crimped wire.
Additionally, the autosampler is operatively connected to an apparatus for puncturing holes into the top of a sealed specimen container. The puncturing apparatus comprises a housing, which is operatively connected to the parent instrument and which is movable between an upper and a lower position. A spring biases the housing into the lower position. A sharp object, such as a pin, is housed inside the housing. When a sealed specimen container is positioned under the sharp object, movement of the tray table to its uppermost position causes the container to force the housing to move from the lower position to the upper position thereby exposing the sharp object. This causes the sharp object to puncture the sealed specimen container.
Additionally, the autosampler is operatively connected to an electrostatic discharge device which reduces or eliminates electrostatic fields which are formed on the surface of glassware of the furnace and on the surface of the autosampler tray and gripper assembly. The electrostatic discharge device comprises a housing which is removably attached to the parent instrument; the housing has a channel thereabout. At least one pin, but preferably a plurality of pins, is positioned inside the housing and in fluid communication with the channel. A source of high voltage alternating current is electrically connected to each pin and supplies voltage to the pins. This generates multiple free ions which cancel the electrostatic field. A source of pressurized gas, such as nitrogen or air, is operatively connected to the housing and forces gas through the channel and around the pins and directs the free ions toward an electrostatic field to neutralize the ions therein.
The invention and its particular features and advantages will become more apparent from the following detailed description when considered with reference to the accompanying drawings.